Neutron activation and detection of hazardous, undesirable, or high value material

ABSTRACT

Provided herein are neutron-based detection systems and methods that provide, for example, high throughput analysis of elemental analysis of scrap materials. Such systems and methods find use for the commercial-scale evaluation of bulk process materials where hazardous or otherwise undesirable materials or high value materials may be interspersed with the primary process material. In certain embodiments, the system is used to detect and potentially remove unexploded ordinance (UXO) from a conveyor of demilitarized shell casings being recycled by detecting the presence of nitrogen and other elements present in the UXO. In other embodiments, the system detects and removes unwanted or highly valuable materials from a stream of scrap material.

The present application is a continuation of U.S. patent applicationSer. No. 16/796,000, filed Feb. 20, 2020, which claims priority to U.S.Provisional Application No. 62/808,330, filed Feb. 21, 2019, which areherein incorporated by reference in their entireties.

FIELD

Provided herein are neutron-based detection systems and methods thatprovide, for example, high throughput elemental analysis of scrapmaterials. Such systems and methods find use for the commercial-scaleevaluation of bulk process materials where hazardous or otherwiseundesirable materials or high value materials may be interspersed withthe primary process material. In certain embodiments, the system is usedto detect and potentially remove unexploded ordinance (UXO) from aconveyor of demilitarized shell casings being recycled by detecting thepresence of nitrogen and other elements present in the UXO. In otherembodiments, the system detects and/or removes unwanted or highlyvaluable materials from a stream of bulk material.

BACKGROUND

The high-level problem is one of improving the efficiency andeffectiveness of identifying and removing hazardous, impure, or highlyvaluable materials from a process stream of material. An example of thisis the ammunition demilitarization processes for US and othermilitaries. The process for demilitarizing small caliber ammunitioninvolves placing rounds in a rotary kiln (or other heating device) andallowing the round to ‘cook-off’ or self-initiate. The ‘cooked-off’rounds are then stored for cool down. In alternative processes the roundis mechanically separated (pulled apart, cut apart, etc.), and theenergetic fill is manually removed. The final destination for thecomponents of the round are typically metals recyclers, disposalfacilities or re-purposing energetic materials into lower gradeenergetic devices. Prior to the material being released to recyclers ordisposal facilities, a quality control step is performed to ensure thematerials do not pose a significant hazard (e.g., there is no energetichazard). The current solution is to perform visual inspection by humanoperators. The current process for this quality control inspection islabor intensive and subjective, potentially resulting in accidents.Improved systems and methods are needed.

SUMMARY

Provided herein are neutron-based detection systems and methods thatprovide, for example, high throughput elemental analysis of scrapmaterials.

For example, in some embodiments, provided herein are compact activeneutron interrogation systems comprising one or more of each of: a) aneutron source assembly configured to produce source neutrons; b) amoderator/shielding assembly surrounding the neutron source; c) a gammaor neutron detector assembly that detects secondary radiation induced bythe neutrons; d) a material handling component that presents bulk orscrap material to a neutron field generated by the neutron sourceassembly and to the gamma or neutron detectors; and e) a computerprocessor configured to identify material of interest from datacollected by said detector assembly and to distinguish material ofinterest from material not of interest. In some embodiments, the systemfurther comprises an alarm component that signals an operator orautomated system to remove material of interest from the bulk or scrapmaterial.

In some embodiments, the neutron source utilizes a deuterium-deuterium(DD) fusion reaction to generate said source neutrons. In someembodiments, the neutron source utilizes a deuterium-tritium (DT) fusionreaction to generate said source neutrons. In some embodiments, theneutron source utilizes a radioactive isotope to generate sourceneutrons. In some embodiments, the neutron source utilizes aproton-beryllium reaction to generate said source neutrons. In someembodiments, the neutron source utilizes a proton-lithium reaction togenerate said source neutrons.

In some embodiments, the processor is configured to identify two or moredifferent materials simultaneously (e.g., two different rare earthmetals). In some embodiments, processor is configured to identify atrace material contained in bulk material. In some embodiments, thetrace material is a trace mineral. In some embodiments, the tracemineral is a rare earth element.

In some embodiments, the system further comprises a bulk material (e.g.,a recycling process stream) on the material handling component.

Also provided herein is a compact active neutron interrogation systemoptimized for the detection of energetic material comprising one or moreor each of: a) a neutron source assembly configured to produce sourceneutrons; b) a moderator/shielding assembly surrounding the neutronsource; c) a gamma or neutron detector assembly that detects secondaryradiation induced by the neutrons; d) a material handling component thatpresents bulk or scrap material to the neutron field and to the gamma orneutron detectors; e) a processor configured to identify energeticcompounds; and f) an alarm that alerts an operator or automated systemto remove the detected energetic material.

In some embodiments, the central neutron source utilizes adeuterium-deuterium (DD) fusion reaction to generate said sourceneutrons. In some embodiments, the central neutron source utilizes adeuterium-tritium (DT) fusion reaction to generate said source neutrons.In some embodiments, the central neutron source utilizes a radioactiveisotope to generate said source neutrons.

In some embodiments, the neutron source utilizes a proton-berylliumreaction to generate said source neutrons. In some embodiments, theneutron source utilizes a proton-lithium reaction to generate saidsource neutrons. In some embodiments, the moderator and structuralmaterial is comprised solely of materials not containing hydrogen,allowing for easier detection of hydrogen in the material being scanned.

In some embodiments, the system further comprises a material locationfeature utilizing either multiple detectors and a triangulation strategyor one or more gamma cameras.

In some embodiments, the system further comprising a mobile platform onwhich the neutron source assembly and/or other components of the systemis mounted.

Further provided herein are methods of using such systems, for example,to analyze a bulk stream of materials to identify and/or isolate one ormore materials of interest away from materials not of interest.

BRIEF DESCRIPTION OF THE DRAWINGS

The patent or application file contains at least one drawing executed incolor. Copies of this patent or patent application publication withcolor drawings will be provided by the Office upon request and paymentof the necessary fee.

FIG. 1 shows an exemplary schematic of a compact active neutroninterrogation system with a central neutron source, moderator assembly,components for presenting bulk material to the neutrons, gamma detectorassembly, software algorithm, and components for alerting an operator toremove the material of interest.

FIG. 2 shows an exemplary computer analysis process for analyzing datagenerated from the systems and methods described herein.

FIG. 3 shows a top-level block diagram of a neutron activation anddetection system.

FIG. 4 shows an exemplary gamma spectrum before (orange) and after(blue) calibration. Dashed lines indicate the first escape of theelement of same color.

FIG. 5 shows and exemplary response function of 3″×3″ LaBr3 crystal withPhoto Multiplier Tube (PMT) for 10.8 MeV incident gamma flux.

FIG. 6 shows an exemplary application of the forward model to matchchlorine lines in PVC. The raw predictive (MCNP code) calculation outputis shown in blue (scaled to a smaller value for clarity). The responsefunction (which changes with energy) is convolved with the MCNPcalculation to predict what will be measured, shown in green. Themeasured data is highlighted in red.

FIG. 7 shows an exemplary Bayesian analysis of measured gamma spectrum,with gamma counts of the 10.8 MeV nitrogen line and the 10.6 MeV siliconline. Dot 1 corresponds to the reference background case, and Dot 2corresponds to IED simulant case. The top left shows the measuredspectrum, and the best fit along with the constituent Si and N parts.The top right shows the final count probability distribution for thenitrogen. The bottom panel shows the 2D probability map for both Si andN.

FIG. 8 shows a description of the Currie detection threshold which isbased off the reference background signal, its standard deviation, andthe standard deviation of the test signal.

FIG. 9 shows an exemplary plot of detected counts versus time forenergetic material being scanned.

FIG. 10 shows the top and side views of an exemplary system fordetecting the location of hazardous material on a conveyor system.

DETAILED DESCRIPTION

Provided herein are systems and methods that improve the efficiency andeffectiveness of identifying and removing hazardous, impure, or highlyvaluable materials from a process stream of material. In someembodiments, the systems and methods employ a neutron source toirradiate scrap materials, radiation detectors to identify whatradiation is emitted from the irradiated scrap, and software algorithmsto review the radiation spectrum and identify the presence of hazardousmaterials based on their radiation signature. This method finds use forany number of applications where an impurity is to be detected in astream of base material.

In some embodiments, the systems and methods provided herein utilize aprompt gamma neutron activation analysis (PGNAA) (REF. 1) measurementtechnique to provide a non-destructive analysis of the composition ofbulk or scrap materials, although many active neutron interrogationtechniques may be employed, such as Thermal Neutron Analysis (REF. 2),Fast Neutron Analysis (REF. 3), or Associated Particle Inspection (REF.4), based on the elemental composition of the bulk and hazardousmaterial. In the PGNAA method, neutrons interact with elements in thematerials, which then emit secondary, prompt gamma rays that aremeasured. Each element emits a unique “fingerprint” of secondary gammaradiation that is used to quantify the composition of the material beingmeasured.

In some embodiments, a neutron source is used to irradiate scrapmaterials, radiation detectors are used to identify what radiation isemitted from the irradiated scrap, software algorithms are used toreview the radiation spectrum and identify the presence of hazardousmaterials based on their radiation signature, and components forseparating the hazardous material from the primary stream of materialare used. An example embodiment is the activation and detection ofnitrogen, which is commonly present in gun powders and other energeticmaterials, based on the emission of a 10.8 MeV gamma ray. Anotherexample embodiment is the activation and detection of hydrogen, which ispresent in energetic materials and in certain corrosion products, basedon the emission of a 2.2 MeV gamma ray. Such example embodiments are ofrelevance to the demilitarization of ammunition and artillery rounds.

In another embodiment, a neutron source is used to irradiate electronicswaste streams and improve the efficiency of the process and quality ofthe extracted materials. Efficient separation of materials is thefoundation of electronics recycling. In the e-waste recycling it iscritical to ensure lead, mercury, cadmium and other heavy metals arekept out of landfills and water sources. Additionally, valuable preciousmetals such as gold, silver and platinum are present in the electronicdevices. Initial shredding of e-waste stream facilitates sorting andseparation of plastics from metals and internal circuitry. Powerfulmagnets separate iron and steel from the waste stream on a conveyor.Further mechanical processing separates aluminum, copper and circuitboards from the material stream which now is mostly plastic. Waterseparation technologies are used to separate glass from plastics. Thefinal step in the separation process locates and extracts any remainingmetal remnants from the plastics to further purify the stream. In thee-waste process, visual inspection and hand sorting are used to improvethe quality of extracted materials. As previously described, theactivation and detection of hydrogen, which is present in plastic, basedon the emission of a 2.2 MeV gamma ray, can allow the separation ofplastics from the metals' streams. In the reverse, ferrous metals can bedetected and separated from plastics streams by the activation of ironand emission of 7.6 MeV gamma rays. The silicon present in the glass canbe activated and detected by the presence of a 4.9 or 10.4 MeV gamma rayto allow the separation of glass from plastics. These detection methodscan improve the efficiency and effectiveness versus visual inspectionand hand sorting. Further, an example embodiment can detect hazardousmaterials in waste streams. For example, lead can be detected by thepresence of 7368 and 3936 keV gamma rays [REF 5]. Cadmium can similarlybe detected by the presence of a 9043 keV gamma peak, amongst others[REF 5]. These and any number of additional materials may be scanned forsimultaneously, each of which has its own unique gamma signature.Scanning for and removing these elements prior to waste entering alandfill provides a further level of environmental protection.

Provided herein are descriptions of industrial scale analysis systemsthat provide a neutron source and moderator assembly coupled to amaterial handling system to move bulk material through the resultantthermal neutron “cloud”, detector systems to capture resultingradiation, algorithms to process the data, and an isolation system toallow removal of unwanted material from the primary stream. An exemplaryconfiguration is shown in FIG. 1 .

In some embodiments, the interrogation process is driven by, forexample, any non-reactor source of high energy neutrons. Embodiments ofthe technology may be employed with a high-energy ion beam generatorsystem such as those described in, U.S. Pat. Publ. No. 2011/0096887,2012/0300890, and 2016/0163495 and U.S. Pat. Nos. 8,837,662 and9,024,261, all of which are herein incorporated by reference in theirentireties. In other cases, a radionuclide-based neutron source, such asCf-252 or PuBe, is used. However, it should be understood that theseinspection techniques may be applied to a wide range of high energyneutron generating technologies such as deuterium-deuterium ordeuterium-tritium tubes, radiofrequency quadrupole linear accelerators(LINAC), and cyclotron or LINAC proton beams coupled with Beryllium orLithium targets.

Neutrons interacting with the process material cause nuclear reactionsto occur, resulting in secondary gamma and/or neutrons to be generated.Each element emits a unique “fingerprint” of secondary gamma (andsometimes neutron) radiation that finds use to quantify the compositionof the material being measured including but not limited to those listedin the table below.

Key Elemental Features & relative Usable Nuclear Available Materialdensity Reactions Signatures CONTRABAND relatively high O (n,n'γ) (alson,n) 6.130 MeV Explosives relatively high N (n_(th),γ)/(n,n'γ)10.80/5.11, 2.31, 1.64 MeV relatively low C (also n,n) 4.43 MeVrelatively low H (n,n'γ) (also n,n) 2.223 MeV (n_(th),γ) Drugsrelatively high C (n,n'γ) (also n,n) as above (Cocaine/ relatively highH (n_(th),γ) as above Heroin) relatively low O (n,n'γ) (also n,n) asabove low-medium Cl (for (n_(th),γ) and (n,n'γ) 6.110 MeV and otherstrong HCl-drugs) lines for Cl MINERALS Ca, Si, Fe, Al, Mg (n_(th),γ)specific capture (-rays, e.g., Cement 6.420 MeV for Ca 4.934 MeV for Si7.630-46 MeV for Fe, etc. Coal C (high concentration) (n_(th),γ),(n,n'γ) specific capture (or inelastic) γ- H, S, Si, Al, Fe, Ca,(n_(th),γ) rays, K, Na, Ti e.g., 4.945 MeV (n,( ) and 4.43 MeV (n,nN( )for C, 2.223 MeV for H, 5.420 MeV for S, etc. NUCLEAR ²³²Th, ²³³U, ²³⁵U,(n_(th),f), (n_(f),f), (γ,f); n_(p), n_(d)(t), γ_(p), γ_(d)(t); alsohigh ²³⁹Pu, ²⁴⁰Pu 2^(nd): (n_(th),γ) (n,n'γ) multiplicity coincidence;very high Z & density

In some embodiments, the fast neutron source is wholly or partiallysurrounded by multiplying and/or moderating material and/or neutroncollimators, such that the neutron flux, energy spectra and beam shapeare tailored to optimize the reaction rate of the material(s) to bedetected while simultaneously minimizing background radiation productionand ensuring safe operations. In certain embodiments, this utilizesseveral inches or feet thicknesses of moderating material to maximallythermalize the neutron population including but not limited to graphite,light water, heavy water, beryllium, or polyethylene. In otherembodiments, the moderator, shielding, and structural materials(including the material handling equipment) are constructed of materialsthat do not contain any hydrogen. This ensures a very low backgroundlevel of 2.2 MeV hydrogen-induced gamma rays such that hydrogenousmaterial (e.g. residual energetic material in ammunition) is more easilydetected.

Detectors are utilized to measure this secondary radiation, includingthe spectrum of gamma energy. The strength, or brightness, of theneutron source should be high enough to allow penetration of the primarystream of material and provide adequate activation of undesirablematerial in order to provide a detectable signal to radiation detectors.A source with a neutron output greater than 1e10 neutrons/second may benecessary in some applications to provide reasonable process throughput.In some embodiments, the hazardous or otherwise interesting gamma peaksare quantified by utilizing standards of know geometry and composition.In certain embodiments, multiple detectors are used to triangulate thelocation of the material of interest by comparing signal intensity. Inother embodiments, detector arrays (potentially collimated) are used togenerate more specific location information. Example detector types thatcould be incorporated into application include but are not limited toinorganic crystal scintillators such as sodium iodide, lanthanumbromide, lanthanum chloride, cesium iodide, cesium fluoride, potassiumiodide, lithium iodide, barium fluoride, calcium fluoride, bismuthgermanate, germanium lithium, zinc sulfide, calcium tungstate, cadmiumtungstate, yttrium aluminium garnet, gadolinium oxyorthosilicate,lutetium iodide, and lutetium oxyorthosilicate or plastic scintillatorslike polyethylene naphthalate, Each of these detectors has specificproperties like detection efficiency, light output and energy resolutionin addition to costs that present benefits and drawbacks fordistinguishing between many radiation signatures. This also more easilyallows for multiple hazardous or non-desirable components to be detectedand tracked simultaneously.

In some embodiments, the radiation spectrum data is post-processed by acomputer and software algorithms identify the presence of hazardous ornon-desirable elements or high value materials based on the knownradiation signatures of isotopes of those elements (See FIG. 2 and FIG.3 ). One option for a post-processing technique is to employ a Bayesianstatistical analysis to estimate parameters material quantities based onthe observed gamma peak distributions.

When employing this technique, a gamma energy calibration would first beperformed. This is accomplished by utilizing a list of times, amplitudesand chi-squared values for calibration data. This is binned into a crudespectrum with a fixed scale factor converting the pulses into units ofMeV. As shown in FIG. 4 , the user then matches the energy peaks ofspecific elements, for example, iron (Fe), hydrogen (H) and copper (Cu)to calibrate the spectrum. Once the calibration has been established,the data is analyzed to measure the gamma peaks of interest, Silicon(Si) and Nitrogen (N) in the example shown in FIG. 4 . The scintillatormaterials used to detect high-energy gammas have the interestingproperty that the maximum response may not be at the input energy. Thisis due to the increasing probability of electron-positron pairproduction. The positron will collide and annihilate within ˜1 ns,releasing two 511 keV photons. The first and second escape peaks (asseen in FIG. 5 ) occur when one or both of those photons are lost. Infact, for a 3″×3″ LaBr₃ crystal, the first escape peak is larger thanthe full-energy photopeak in the energy range of interest.

The detector response varies with incident energy and detector size. Ananalysis code, such as the Monte Carlo Neutral Particle (MCNP) code,returns the response function as a function of energy. The responsefunction may be used as a forward model. An example using calibrationwith chlorine and low intensity Cf-232 source (˜2.5×10⁵ n/s) is shown inFIG. 6 .

In the Bayesian analysis strategy, a forward model (F) for the NaI andLaBr₃ detectors is utilized. Given a concentration of Si or N (forexample), a prediction of gamma counts (D_(k)) in given energy bins(E_(k)) can be computed where k is used as the index of the energy bin.

D_(k) = Si * [F_(LaBr 3)(E_(Si))]_(k) + N * [F_(LaBr 3)(E_(N))]_(k)

The photon distribution in a given energy bin is binomial, so theprobability of a given photon count (measurement “M” counts) in a givenbin can be computed as a function of concentration of silicon (Si) andnitrogen (N).

${{Prob}\left( {{{M_{k}\bigvee\ S}i},N} \right)} = \frac{D_{k}^{M_{k}}e^{- D_{k}}}{M_{k}!}$Bayes' theorem is applied at this point to compute the probability ofSi, N concentration given the M photon measurements in each k bin:

${{Prob}\left( {{Si},{N\bigvee M_{k}}} \right)} \propto {\prod\limits_{k_{10{MeV}}}^{k_{11.1{MeV}}}\;{{{Prob}\left( {{M_{k}\bigvee{Si}},N} \right)} \times {{Prob}\left( {{Si},{N❘I}} \right.}}}$The last term is the prior probability. At the very start this could bebased on data available from other measurements or even a uniforminitial guess. One implementation calculates the logarithm above as itis more stable, at the end the inverse is performed. As more data iscollected, the probability evolves. Once all the data has beenevaluated, a probability for Si and N respective gamma count is given. Asummary of the result of the Bayesian analysis is shown in FIG. 7 . Theenergetic material in this example displaces sand, this causes a drop inthe silicon signal (a “silicon hole”), and an increase in the nitrogensignal.

Both background and test signals have variations due to signal noise.For a given measured photon count the primary error is the Poisson noisein the photon count. Other sources of noise, for example drift in thespectral calibration, background counts due to external sources (e.g.activation of objects in the vicinity of the detectors) and pulsepile-up, are harder to quantify. The criterion used to distinguish highnitrogen content from background was the Currie detectability threshold.This accounts for variation in the reference background measurement, andalso variation in the test signal measurement. The Currie detectabilitythreshold is widely used in the chemical and nuclear industries and wasdeveloped by L. A. Currie at the National Bureau of Standards in 1968[REF. 6]. The procedure is illustrated in FIG. 8 . The referencebackground, its standard deviation, and the standard deviation of thetest signal contributes to the detection threshold. As a function oftime the reference count, the test signal, and the detection thresholdevolve over time. When the test signal is higher than the detectionthreshold, then a material with high nitrogen content has been detected.A graph of example signal counts over time is shown in FIG. 9 .

In some embodiments, a series of gamma detectors can be utilizedsimultaneously to identify the location of a material being detected.When the material of interest is irradiated with neutrons and emitsgamma radiation, the intensity of that radiation decreases as distancefrom the material squared. This concept is depicted in FIG. 10 . Bycomparing the relative intensity of the gamma signatures via theprocessing algorithm, the location of the material relative to thedetectors can be computed in real time. This information can then beprovided to the operators or a secondary sorting system to isolate thematerial. Another embodiment of this concept would utilize a “gammacamera” such as those currently employed in the medical and certainindustrial fields. The gamma camera would be configured to seek the“image” of the emittance of individual gamma energy peaks. These gammacameras are most effective when capturing images of low energy gammarays, and so may not be applicable when detecting certain elements thatemit higher energy gammas.

Once a hazardous item is identified, the system notifies an operator toremove the item from the process stream. In other embodiments, thesoftware interfaces to a mechanical sorting mechanism that automaticallyremoves the identified material to a separate area away from the mainprocess stream. This separation is accomplished via any number ofmechanical mechanisms. A secondary scan of the material or passage ofthe material over a secondary set of radiation detectors can also beperformed to ensure hazardous item has been removed from the processingstream.

CITATIONS

-   1) PGNAA    -   Published: Sep. 1, 1998    -   Richard M. Lindstrom    -   Proceedings of the Korea Atomic Energy Research Institute Cold        Neutron Workshop    -   https://www.nist.gov/publications/prompt-gamma-neutron-activation-analysis?pub_id=903948    -   https://www.ncnr.nist.gov/instruments/pgaa/-   2) TNA    -   Thermal neutron analysis (TNA) explosive detection based on        electronic neutron generators, W. C. Lee D. B. Mahood P. Ryge P.        Shea T. Gozani,    -   Nuclear Instruments and Methods in Physics Research Section B:        Beam Interactions with Materials and Atoms    -   Volume 99, Issues 1-4, 5 May 1995, Pages 739-742    -   https://www.sciencedirect.com/science/article/pii/0168583X95002219-   3) FNAA    -   Source: Element Analysis Corporation    -   https://www.chemicalonline.com/doc/fast-neutron-activation-analysis-fnaa-0001-   4) API    -   Design of an associated particle imaging system    -   Albert Beyerle J. Paul Hurley Laura Tunnell    -   Nuclear Instruments and Methods in Physics Research Section A:        Accelerators, Spectrometers, Detectors and Associated Equipment    -   Volume 299, Issues 1-3, 20 Dec. 1990, Pages 458-462    -   https://www.sciencedirect.com/science/article/pii/016890029090825Q?via%3Dihub-   5) Database of Prompt Gamma Rays from Slow Neutron Capture for    Elemental Analysis. International Atomic Energy Agency. Vienna, 2007-   6) Limits for Qualitative Detection and Quantitative Determination.    Lloyd A. Currie. Analytical Chemistry, Vol. 40, No. 3, March 1968

We claim:
 1. A compact active neutron interrogation system comprising:a) a neutron source assembly configured to produce source neutrons; b) amoderator/shielding assembly surrounding the neutron source; c) a gammaor neutron detector assembly that detects secondary radiation induced bythe neutrons; d) a material handling component that presents bulk orscrap material to a neutron field generated by the neutron sourceassembly and to the gamma or neutron detectors; and e) a computerprocessor configured to identify material of interest from datacollected by said detector assembly and to distinguish material ofinterest from material not of interest; wherein the bulk or scrapmaterial comprises a recycling process stream, and wherein the materialof interest is lead, mercury, or cadmium.
 2. The system of claim 1,further comprising an alarm component that signals an operator orautomated system to remove material of interest from the bulk or scrapmaterial.
 3. The system of claim 1, where the neutron source utilizes adeuterium-deuterium (DD) fusion reaction to generate said sourceneutrons.
 4. The system of claim 1, where the neutron source utilizes adeuterium-tritium (DT) fusion reaction to generate said source neutrons.5. The system of claim 1, where the neutron source utilizes aradioactive isotope to generate source neutrons.
 6. The system of claim1, where the neutron source utilizes a proton-beryllium reaction togenerate said source neutrons.
 7. The system of claim 1, where theneutron source utilizes a proton-lithium reaction to generate saidsource neutrons.
 8. The system of claim 1, where the processor isconfigured to identify two or more different materials of interestsimultaneously.
 9. The system of claim 1, where the recycling stream isan electronics waste stream.
 10. The system of claim 1, where themoderator/shielding assembly is comprised solely of materials notcontaining hydrogen.
 11. A compact active neutron interrogation systemcomprising: a) a neutron source assembly configured to produce sourceneutrons; b) a moderator/shielding assembly surrounding the neutronsource; c) a gamma or neutron detector assembly that detects secondaryradiation induced by the neutrons; d) a material handling component thatpresents bulk or scrap material to a neutron field generated by theneutron source assembly and to the gamma or neutron detectors; and e) acomputer processor configured to identify material of interest from datacollected by said detector assembly and to distinguish material ofinterest from material not of interest; wherein the bulk or scrapmaterial comprises a recycling process stream, and wherein the materialof interest is gold, silver, or platinum.
 12. The system of claim 11,further comprising an alarm component that signals an operator orautomated system to remove material of interest from the bulk or scrapmaterial.
 13. The system of claim 11, where the processor is configuredto identify two or more different materials of interest simultaneously.14. The system of claim 11, where the recycling stream is an electronicswaste stream.
 15. The system of claim 11, where the moderator/shieldingassembly is comprised solely of materials not containing hydrogen.
 16. Acompact active neutron interrogation system comprising: a) a neutronsource assembly configured to produce source neutrons; b) amoderator/shielding assembly surrounding the neutron source; c) a gammaor neutron detector assembly that detects secondary radiation induced bythe neutrons; d) a material handling component that presents bulk orscrap material to a neutron field generated by the neutron sourceassembly and to the gamma or neutron detectors; and e) a computerprocessor configured to identify material of interest from datacollected by said detector assembly and to distinguish material ofinterest from material not of interest; wherein the bulk or scrapmaterial comprises a recycling process stream, and wherein the materialof interest is a rare earth element.
 17. The system of claim 16, furthercomprising an alarm component that signals an operator or automatedsystem to remove material of interest from the bulk or scrap material.18. The system of claim 16, where the processor is configured toidentify two or more different materials of interest simultaneously. 19.The system of claim 16, where the recycling stream is an electronicswaste stream.
 20. The system of claim 16, where the moderator/shieldingassembly is comprised solely of materials not containing hydrogen.